n-type silicon

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n-type silicon

The use of n-type and p-type silicon is a foundation concept in the design of transistors. Pure silicon is not conductive. However, it can be made conductive by adding other elements to its crystalline structure, which then become known as "n-type" or "p-type" silicon.

The interaction of n-type and p-type silicon to electric fields and to each other is used to make areas in a transistor change from conductive to non-conductive and vice versa (see crystalline semiconductor). See FET, MOSFET, bipolar transistor and doping.

N-Type (Negative)
N-type silicon is silicon that has been chemically combined (doped) with phosphorus gas to make it conductive. A silicon atom has four electrons in its outer shell and bonds tightly with four surrounding silicon atoms creating a crystal matrix with eight electrons in the outer shells. However, phosphorus has five electrons, and when combined, the fifth electron becomes a "free" electron that moves easily within the crystal when a voltage is applied. Because the charge carriers are electrons, n-type refers to a negative charge.

P-Type (Positive)
In contrast, p-type silicon is silicon doped with boron gas that turns it into a conductive material that readily accepts electrons when voltage is applied. Boron has only three electrons in its outer shell and can bond with only three of the four surrounding silicon atoms. This leaves one silicon atom with a vacant location in its outer shell, called a "hole," that readily accepts an electron. Because the charge carriers are holes, p-type silicon is said to have a positive charge.

N-Type and P-Type
This is a very conceptual illustration of the atomic structure of n-type and p-type silicon. (Image courtesy of TechBites Interactive.)
References in periodicals archive ?
Specific topics include the in-situ assessment of macro-pore growth in low-doped n-type silicon, novel morphology-dependent ferromagnetic behavior of meso-porous silicon, electric field effects on the formation of isolated macro-porous silicon, resonant energy transfer from porous silicon to iodine molecules, stain etching with ferric ion to produce thick porous silicon films, and growing a porous layer on n-type indium phosphide in liquid ammonia.
An improvement of 20 to 30 percent in n-type silicon germanium was recently achieved by doping it with gallium phosphide, which decreases the electrical resistivity and increases S[.